Detection of Bovine Viral Diarrhea virus infection in newborn calves before colostrum intake

Abstract

The detection of Bovine Viral Diarrhea virus (BVDV) infection, especially among persistently infected calves (PI), should be performed earlier in order to eliminate the source of the infection and to prevent the spread of the disease in the herd. However, colostrum intake can influence the results of some of the tests used to diagnose the BVDV infection. Therefore, this study evaluated the efficacy of serum neutralization (SN) test in conjunction with reverse transcription-polymerase chain reaction (RT-PCR) for the diagnosis of BVDV infection before colostrum intake. The deliveries of the animals were assisted to select 52 newborn Holstein calves for inclusion in the study. Initially, the whole blood and serum samples were collected from the calves before (T0) and after (T1) the colostrum intake. The calves that were RT-PCR positive at any of the time-points were retested on the 30th day post birth (T2). The presence of specific antibodies for BVDV was evaluated by SN, and that of viral RNA by the RT-PCR. The BVDV-specific antibodies were observed in the serum of 13.46% (7/52) of the calves at T0 because of fetal infection. At T1, seroconversion was observed in 100% (52/52) of the calves. The geometric mean titers (GMT) of the antibodies for BVDV increased significantly from T0 (14.52) to T1 (2490) (P = 0.0001). Of the four calves that were RT-PCR positive before colostrum intake (T0), two were seronegative and two, seropositive. Of the forty-eight RT-PCR negative calves, five were seropositive. After 30 days post birth, all of the animals tested negative by RT-PCR, thus excluding the possibility of persistent infection. The association observed between the results of the SN and RT-PCR assays at T0 (P = 0.025) could not be observed at T1 (P > 0.05). The SN test before the colostrum intake allowed the detection of fetal infection in the herd; however, this test was ineffective as a diagnostic method after the transfer of passive immunity. The confirmation of the results of the SN assay by those of the RT-PCR was essential for the identification of the infected calves before colostrum intake.